1. Field of the Invention
The present invention relates to a method for individually bonding inner leads installed on a tab tape to electrodes of semiconductor devices by a bonding tool and also to an ultrasonic bonding apparatus that uses the method.
2. Prior Art
As shown in FIG. 6(a), inner lead of inner lead rows 2a, 2b, 2c and 2d of a tab tape 1 are installed so that they stick into a squire opening of the tab tape 1. The leads project at right angles form each of the four sides of the opening in the X and Y directions. The leads of inner lead rows 2a through 2d of the tab tape 1 are as shown in FIG. 6(b) individually bonded to electrodes 3a of a semiconductor device 3 when ultrasonic waves are applied to the bonding tool 4 that is at the tip end of horn 5.
The direction of the ultrasonic vibration of the horn 5 is set so that it is in the same direction as the axis of the horn 5. In conventional methods, therefore, the direction of the horn 5 needs to be shifted to match the direction of all the leads of inner lead rows 2a through 2d so that the ultrasonic waves are uniformly applied to the leads of each of the inner lead rows 2a through 2d. This will be described below in more detail.
First, any positional discrepancy between the inner leads of rows 2a through 2d and the electrodes 3a is detected by a detection means (not shown), and then the positions of the inner leads and electrodes are aligned to eliminate the discrepancy. The bonding action by the bonding tool 4 which is at the end of the horn 5 starts with the right-end inner lead 2a-1 of the inner lead row 2a (see FIG. 6(a)). The alignment of the horn 5 is in the Y direction. The bonding tool 4 is lowered to press the inner lead 2a-1 against the corresponding electrode 3a, and an ultrasonic vibration is applied to the horn 5. The inner lead 2a-1 and electrode 3a are thus bonded together. The, the bonding tool 4 is raised and moved in the X direction so that it is above the next inner lead 2a-2. The inner lead 2a-2 and the corresponding electrode 3a are bonded by the same manner as that described above.
When the bonding of all the inner lead of the row 2a has been completed, the horn 5 is rotated to shift 90 degrees so that the axial direction of the horn 5 is brought into the same direction as the inner leads of inner lead row 2b. The inner leads of the row 2b are bonded in the same manner as the inner leads of the row 2a are bonded.
When the bonding of the inner leads of the row 2b is completed, the horn 5 is again shifted 90 degrees so that it can bond the inner leads of row 2c. The inner leads of the row 2c are bonded in the same manner as described above. When the bonding on the inner leads of row 2c is completed, the horn 5 is shifted 90 degrees, and the inner leads of row 2d are bonded. When the bonding of the inner leads of the row 2d is finished, the horn 5 is again shifted 90 degrees, thus returning to the starting position.
As seen from the above, the horn 5 is shifted four times in direction (90 degrees each time and totally 360 degrees) in order to perform the bonding of all the inner leads to a single semiconductor device.
One example of ultrasonic bonding apparatus that rotates the horn 360 degrees as described above is shown in Japanese Patent Application Publication No. 62-27741 .
The bonding apparatus disclosed in this Publication includes (a) a horn that holds a bonding tool, (b) a rotary shaft which is installed coaxially with the bonding tool and indirectly holds the horn, (c) a vertically moving block which rotatably supports the rotary shaft, (d) a vertically driving mechanism that moves the vertically moving block up and down, and (e) a rotary driving mechanism that rotates the rotary shaft. The rotary driving mechanism rotates the rotary shaft via a belt system installed between a pulley of an output shaft of the motor for the rotary driving mechanism and a pulley of the rotary shaft.
In this apparatus, the horn must be shifted four times for each semiconductor device. This results in waste of time, keeping the productivity very low.
Furthermore, in the above ultrasonic bonding apparatus, a motor is used to rotate the rotary shaft, and it needs a heavy-weight vertically moving block to mount the motor thereon. As a result, excessive force applies not only the vertically driving mechanism, that moves the vertically moving block up and down, but also onto an X-Y table driving mechanism, which moves the vertically moving block in the X-Y direction. Furthermore, since the motor controls the 90 degree rotation of the rotary shaft, the control system is complicated. In addition, the precision of rotation of the rotary shaft is easily affected by a slippage of the belt that transmits the rotation of the motor to the rotary shaft.